{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,13]],"date-time":"2026-03-13T17:31:27Z","timestamp":1773423087121,"version":"3.50.1"},"reference-count":19,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2025,12,13]],"date-time":"2025-12-13T00:00:00Z","timestamp":1765584000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Viruses"],"abstract":"<jats:p>Although vaccination for COVID-19 and mask wearing were two of the main preventive measures against infection, their impact is unclear. In the present study, by using national surveillance data in Japan, we compared the incidence rate and weekly case increase ratios of COVID-19 with the domestic stocks of masks and vaccination coverage. The trajectory of epidemic growth increased rapidly in the summer of 2021, concomitant with the launch of the mass national vaccination program. The most rapid spread of the epidemic was found in 2022, approximately 6 months after the national mass vaccination started, with the emergence of the Omicron variant. From 2022, two annual epidemic peaks occurred with seasonal changes. Whilst the winter peak follows the expected seasonal trend in respiratory infections, the summer peak may reflect a combination of short-term herd immunity and behavioral patterns. Nevertheless, these epidemic peaks continued irrespective of vaccine coverage and mask use. Further analysis into the duration of protective efficacy of the vaccines and mask use is required.<\/jats:p>","DOI":"10.3390\/v17121612","type":"journal-article","created":{"date-parts":[[2025,12,15]],"date-time":"2025-12-15T09:36:39Z","timestamp":1765791399000},"page":"1612","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["COVID-19 Double Annual Epidemic Peaks in Summer and in Winter from 2022, Irrespective of the Rate of Mask Wearing and Vaccination"],"prefix":"10.3390","volume":"17","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0247-0623","authenticated-orcid":false,"given":"Shinako","family":"Inaida","sequence":"first","affiliation":[{"name":"Laboratory of Integrative Molecular Medicine, Graduate School of Medicine, Kyoto University, Kyoto 606-8303, Japan"},{"name":"Department of Preventive Medicine and Behavioral Science, Kindai University Faculty of Medicine, Osaka 590-0197, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0665-5089","authenticated-orcid":false,"given":"Richard E.","family":"Paul","sequence":"additional","affiliation":[{"name":"Pasteur Kyoto International Joint Research Unit for Integrative Vaccinomics, Kyoto 606-8303, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8536-8653","authenticated-orcid":false,"given":"Minsoo","family":"Kim","sequence":"additional","affiliation":[{"name":"Laboratory of Integrative Molecular Medicine, Graduate School of Medicine, Kyoto University, Kyoto 606-8303, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,12,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"e068302","DOI":"10.1136\/bmj-2021-068302","article-title":"Effectiveness of public health measures in reducing the incidence of covid-19, SARS-CoV-2 transmission, and covid-19 mortality: Systematic review and meta-analysis","volume":"375","author":"Talic","year":"2021","journal-title":"BMJ"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"e108","DOI":"10.1093\/cid\/ciac635","article-title":"Coronavirus Disease 19 (COVID-19) Vaccine Effectiveness Against Symptomatic Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection During Delta-Dominant and Omicron-Dominant Periods in Japan: A Multicenter Prospective Case-control Study (Factors Associated with SARS-CoV-2 Infection and the Effectiveness of COVID-19 Vaccines Study)","volume":"76","author":"Arashiro","year":"2023","journal-title":"Clin. Infect. Dis."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1161","DOI":"10.1038\/s41564-022-01143-7","article-title":"SARS-CoV-2 Omicron is an immune escape variant with an altered cell entry pathway","volume":"7","author":"Willett","year":"2022","journal-title":"Nat. Microbiol."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1207","DOI":"10.1056\/NEJMoa2118691","article-title":"Protection against SARS-CoV-2 after Covid-19 Vaccination and Previous Infection","volume":"386","author":"Hall","year":"2022","journal-title":"N. Engl. J. Med."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"123792","DOI":"10.1016\/j.envpol.2024.123792","article-title":"Disposable surgical\/medical face masks and filtering face pieces: Source of microplastics and chemical additives in the environment","volume":"348","author":"Bogush","year":"2024","journal-title":"Environ. Pollut."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"134219","DOI":"10.1016\/j.jhazmat.2024.134219","article-title":"Potential health risks of microplastic fibres release from disposable surgical masks: Impact of repeated wearing and handling","volume":"470","author":"Weng","year":"2024","journal-title":"J. Hazard. Mater."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1114","DOI":"10.1038\/s41591-024-03453-1","article-title":"Bioaccumulation of microplastics in decedent human brains","volume":"31","author":"Garcia","year":"2025","journal-title":"Nat. Med."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"S14","DOI":"10.2188\/jea.17.S14","article-title":"Epidemics of influenza and pediatric diseases observed in infectious disease surveillance in Japan, 1999\u20132005","volume":"17","author":"Ohta","year":"2007","journal-title":"J. Epidemiol."},{"key":"ref_9","unstructured":"(2025, April 20). Infectious Diseases Weekly Report (IDWR). Available online: https:\/\/www.niid.go.jp\/niid\/en\/idwr-e.html."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"12026","DOI":"10.1038\/s41598-022-15867-3","article-title":"Longitudinal surveillance of influenza in Japan, 2006\u20132016","volume":"12","author":"Inaida","year":"2022","journal-title":"Sci. Rep."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1070","DOI":"10.1016\/j.ajic.2022.05.009","article-title":"Viral transmissibility of SARS-CoV-2 accelerates in the winter, similarly to influenza epidemics","volume":"50","author":"Inaida","year":"2022","journal-title":"Am. J. Infect. Control"},{"key":"ref_12","unstructured":"(2025, April 20). Yearly Mask Stock in Japan, Hygiene Products Industry Association. (In Japanese)."},{"key":"ref_13","unstructured":"(2025, April 20). COVID-19 Vaccination Coverage in Japan. Available online: https:\/\/www.niid.go.jp\/niid\/ja\/2019-ncov\/2484-idsc\/10840-covid19-64.html."},{"key":"ref_14","unstructured":"(2025, April 20). COVID-19 Vaccination Data in Japan, Ministry of Health, Labour, Welfare. Available online: https:\/\/www.mhlw.go.jp\/stf\/seisakunitsuite\/bunya\/kenkou_iryou\/kenkou\/kekkaku-kansenshou\/yobou-sesshu\/syukeihou_00002.html."},{"key":"ref_15","unstructured":"(2025, April 20). COVID-19 Vaccination Data in Japan, NHK Web. Available online: https:\/\/www3.nhk.or.jp\/news\/special\/coronavirus\/vaccine\/."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"704","DOI":"10.1016\/S1473-3099(04)01177-6","article-title":"Seasonality of infectious diseases and severe acute respiratory syndrome\u2014What we don\u2019t know can hurt us","volume":"4","author":"Dowell","year":"2004","journal-title":"Lancet Infect. Dis."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"e149","DOI":"10.1016\/S2666-5247(22)00290-7","article-title":"COVID-19 lateral flow IgG seropositivity and serum neutralising antibody responses after primary and booster vaccinations in Chile: A cross-sectional study","volume":"4","author":"Torres","year":"2023","journal-title":"Lancet Microbe"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Orlandi, C., Stefanetti, G., Barocci, S., Buffi, G., Diotallevi, A., Rocchi, E., Ceccarelli, M., Peluso, S., Vandini, D., and Carlotti, E. (2023). Comparing Heterologous and Homologous COVID-19 Vaccination: A Longitudinal Study of Antibody Decay. Viruses, 15.","DOI":"10.3390\/v15051162"},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Bahrami, F., Batt, T., Schudel, S., Annaheim, S., He, W., Wang, J., Rossi, R.M., and Defraeye, T. (2022). How long and effective does a mask protect you from an infected person who emits virus-laden particles: By implementing one-dimensional physics-based modeling. Front. Public Health, 10.","DOI":"10.3389\/fpubh.2022.991455"}],"container-title":["Viruses"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1999-4915\/17\/12\/1612\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,12,17]],"date-time":"2025-12-17T09:48:16Z","timestamp":1765964896000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1999-4915\/17\/12\/1612"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,12,13]]},"references-count":19,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2025,12]]}},"alternative-id":["v17121612"],"URL":"https:\/\/doi.org\/10.3390\/v17121612","relation":{},"ISSN":["1999-4915"],"issn-type":[{"value":"1999-4915","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,12,13]]}}}